Overview

Serial communication interfaces are commonly used to exchange data with other computers. Serial interfaces are ubiquitous, because they are economical to implement over long distances as a result of their requirement of relatively few wires. Many types of serial interfaces have been developed, with speeds ranging to billions of bits per second. Regardless of the bit rate, serial communication interfaces share many common traits. This chapter introduces the fundamentals of serial communication in the context of popular data links such as RS-232 and RS-485 in which bandwidths and components lend themselves to basic circuit fabrication techniques.

The chapter first deals with the basic parallel-to-serial-to-parallel conversion process that is at the heart of all serial communication. Wide buses must be serialized at the transmitter and reconstructed at the receiver. Techniques for accomplishing this vary with the specific type of data link, but basic concepts of framing and error detection are universal.

Two widely deployed point-to-point serial communication standards, RS-232 and RS-422, are presented, along with the standard ASCII character set, to see how theory meets practice. Standards are important to communications in general because of the need to connect disparate equipment. ASCII is one of the most fundamental data representation formats with global recognition. RS-232 has traditionally been found in many digital systems, because it is a reliable standard. Understanding RS-232, its relative RS-422, and ASCII enables an engineer to design a communication interface that can work with an almost infinite range of complementary equipment ranging from computers to modems...